Interpretive Summary: Butterfly bush (Buddleja davidii) is considered an invasive weed in parts of Europe, Australia, and the U.S. Little research has addressed methods for controlling butterfly bush invasions. The objective of this research was to evaluate several herbicides and two application methods for controlling butterfly bush postemergence.
The following herbicides were either sprayed or painted on recently cut stumps of butterfly bush: Roundup Ultramax (glyphosate + surfactant), Aquamaster (glyphosate), Arsenal (imazapyr), and Garlon (triclopyr). Applications were made in late summer to both small (12 to 14 in tall) and large (5 to 6 ft tall) plants. Roundup and Aquamaster provided the most rapid control, although all herbicides provided 100% control when plants were evaluated the following spring. Spray applications are easier to make on small plants, but cut-stump applications are more precise when applications are made near sensitive ecosystems. As all herbicides and both application methods were 100% effective, site conditions should dictate which herbicide or application method is used.

Technical Abstract:
Butterfly bush (Buddleja davidii) is classified as invasive in several parts of the United States. Two experiments were conducted to evaluate the effectiveness of four herbicides and two application methods on postemergence butterfly bush control. The four herbicides included: Roundup (glyphosate), Aquamaster (glyphosate), Garlon (triclopyr), and Arsenal (imazapyr). Application methods included spraying foliage with a CO2 backpack sprayer, and applying herbicide concentrate to recently cut stems (cut-stump method). Plants were treated in September with the maximum labeled rate for each herbicide. Cut-stump rates were determined such that the same amount of active ingredient was applied as in the spray treatments. Applications were made to plants several months after planting to simulate control of small recently germinated plants, and again to plants over 1 year old to simulate control of larger and more established plants. Summarizing results over both plant sizes and from two repetitions of the experiment, Roundup and Aquamaster provided higher levels of control compared to Garlon and Arsenal early in the experiment. Cut-stump applications provided more rapid control than spray applications. Despite differences in control when evaluated several weeks after application, all treated plants were dead when evaluated the following spring.